1. Field of the Invention
The present invention relates to a thin-film magnetic head, a head gimbal assembly (HGA) with a thin-film magnetic head, a magnetic disk drive apparatus with the HGA, a method for designing a thin-film magnetic head, and a manufacturing method of a thin-film magnetic head.
2. Description of the Related Art
In a magnetic disk drive apparatus, one or more thin-film magnetic heads write signals into and read signals from one ore more magnetic disk rotated by a spindle motor. Each thin-film magnetic head has a slider as a main body fixed at a top end section of a suspension of an HGA, and has an inductive write head element and a magnetoresistive effect (MR) read head element formed on this slider. When writing or reading, the thin-film magnetic head is driven to a desired position on the magnetic disk by an arm capable of swinging.
When writing or reading signals, the thin-film magnetic head aerodynamically flies with keeping a predetermined magnetic spacing above the surface of the rotating magnetic disk. In this flying state, the thin-film magnetic head performs writing of signals to the magnetic disk using magnetic field generated from the inductive write head element, and performs reading of signals by sensing a magnetic field from the magnetic disk using the MR read head element.
Recently, a track width of a thin-film magnetic head becomes narrower to satisfy the requirements for increasing data storage capacities and densities of a magnetic disk drive apparatus. If the track width becomes narrow, writing ability of the magnetic write head element and also reading ability of the magnetic read head element decline. On the other hand, due to the recent increase in recording densities, recording bits on the written magnetic disk become very small. Thus, it is required for the magnetic write head element and the MR read head element to have much higher performance.
In order to solve such problems of the writing and/or reading performance, recent magnetic disk drive apparatus tends to have a smaller magnetic spacing. That is because, as smaller the spacing becomes, the signal magnetic field from the magnetic disk received in the thin-film magnetic head becomes stronger. Therefore, the magnetic disk drive apparatus is designed such that the magnetic spacing between the thin-film magnetic head and the magnetic disk surface becomes very small to satisfy today's increasing recording density.
However, when writing, Joule heat caused by a write signal current generates from a coil layer in the inductive write head element, and moreover, heat caused by an eddy current loss will be generated in upper and lower pole layers in the inductive write head element. This generated heat is accumulated inside of the magnetic head, and thus an overcoat layer or an insulation film expands thermally, to lead to a TPTP (Thermal Pole Tip Protrusion) phenomenon wherein the inductive write head element and the MR read head element protrude toward the magnetic disk surface. In this case, if a designed value of the magnetic spacing is very small, the protruded part of the MR read head element may contact the surface of the magnetic disk. This may lead to frictional heat causing change in the electric resistance value of the MR read head element to produce an abnormal read out signal or thermal asperity.
In order to avoid such thermal asperity, several methods for controlling magnetic spacing have been proposed. For example, U.S. Pat. No. 5,991,113 discloses a slider having a transducer or a magnetic head element, and a heater formed, adjacent to the transducer, in the slider body or between the slider body and the transducer. The heater is heated by applying current there through, and the transducer is protruded due to the difference in expansion coefficients between a transducer-formed region including a protection layer and the slider body so as to control the magnetic spacing.
US patent publication No. 2003/174430 discloses a thin-film magnetic head structure with a read head element, a write head element and a thermally expansive element for bringing the read head element and the write head element close to a magnetic disk surface when current flow a heater. In this structure, the heater and the thermally expansive element are arranged in a pair. When the heater is energized, the thermally expansive element arranged in a pair expands to distort an overcoat layer of the magnetic head so that the read head element and the write head element are brought close to the magnetic disk surface.
US patent publication No. 2003/99054 discloses a thin-film magnetic head with a heating means arranged at the opposite of an air bearing surface (ABS) of a magnetic head element. When the magnetic head element is in operation, the heating means is heated so that the magnetic head element protrudes toward the ABS direction to adjust a magnetic spacing.
However, in such thin-film magnetic heads provided with the pair of heater and thermally expansive element or with the heating means, or a thin-film magnetic head provided with no heater but thermally expanded by the heat of its inductive write head element, because the generated heat and stress are applied to the MR read head element, shortening in lifetime, or change in characteristic or instability caused by the stress change under high temperature sometimes occur.
In the conventional methods for controlling the magnetic spacing of such thin-film magnetic heads, there has been almost no measure to maintain the temperature increase of the MR read head element.